gonum.org/v1/gonum@v0.14.0/lapack/gonum/dlauu2.go (about)

     1  // Copyright ©2018 The Gonum Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package gonum
     6  
     7  import (
     8  	"gonum.org/v1/gonum/blas"
     9  	"gonum.org/v1/gonum/blas/blas64"
    10  )
    11  
    12  // Dlauu2 computes the product
    13  //
    14  //	U * Uᵀ  if uplo is blas.Upper
    15  //	Lᵀ * L  if uplo is blas.Lower
    16  //
    17  // where U or L is stored in the upper or lower triangular part of A.
    18  // Only the upper or lower triangle of the result is stored, overwriting
    19  // the corresponding factor in A.
    20  func (impl Implementation) Dlauu2(uplo blas.Uplo, n int, a []float64, lda int) {
    21  	switch {
    22  	case uplo != blas.Upper && uplo != blas.Lower:
    23  		panic(badUplo)
    24  	case n < 0:
    25  		panic(nLT0)
    26  	case lda < max(1, n):
    27  		panic(badLdA)
    28  	}
    29  
    30  	// Quick return if possible.
    31  	if n == 0 {
    32  		return
    33  	}
    34  
    35  	if len(a) < (n-1)*lda+n {
    36  		panic(shortA)
    37  	}
    38  
    39  	bi := blas64.Implementation()
    40  
    41  	if uplo == blas.Upper {
    42  		// Compute the product U*Uᵀ.
    43  		for i := 0; i < n; i++ {
    44  			aii := a[i*lda+i]
    45  			if i < n-1 {
    46  				a[i*lda+i] = bi.Ddot(n-i, a[i*lda+i:], 1, a[i*lda+i:], 1)
    47  				bi.Dgemv(blas.NoTrans, i, n-i-1, 1, a[i+1:], lda, a[i*lda+i+1:], 1,
    48  					aii, a[i:], lda)
    49  			} else {
    50  				bi.Dscal(i+1, aii, a[i:], lda)
    51  			}
    52  		}
    53  	} else {
    54  		// Compute the product Lᵀ*L.
    55  		for i := 0; i < n; i++ {
    56  			aii := a[i*lda+i]
    57  			if i < n-1 {
    58  				a[i*lda+i] = bi.Ddot(n-i, a[i*lda+i:], lda, a[i*lda+i:], lda)
    59  				bi.Dgemv(blas.Trans, n-i-1, i, 1, a[(i+1)*lda:], lda, a[(i+1)*lda+i:], lda,
    60  					aii, a[i*lda:], 1)
    61  			} else {
    62  				bi.Dscal(i+1, aii, a[i*lda:], 1)
    63  			}
    64  		}
    65  	}
    66  }